1. Technical Field
The present invention relates to a seat belt retractor, and particularly relates to a seat belt retractor including a torsion bar for absorbing energy of a vehicle occupant.
2. Description of the Prior Art
A known vehicle seat belt retractor includes seat belt webbing wound on a spool of the retractor. A spool locking mechanism for the retractor includes a ratchet rotatable with the spool and a pawl. The pawl is movable into engagement with the ratchet to block rotation of the ratchet. This actuation of the spool locking mechanism blocks withdrawal of seat belt webbing from the spool, to help protect a vehicle occupant in the event of a vehicle collision.
The retractor includes a torsion bar acting between the spool and the ratchet. When the spool locking mechanism is actuated, and the occupant moves forward against the seat belt webbing with sufficient force, the kinetic energy of the occupant is transmitted through the spool into the torsion bar and the ratchet. The torsion bar begins to twist when a given load is applied to the belt webbing. The twisting of the torsion bar allows the spool to rotate relative to the ratchet and allows a small amount of belt webbing to pay out. This release of belt webbing permits a small amount of additional forward movement of the vehicle occupant and reduces the peak load on the occupant.
The present invention is a seat belt retractor comprising a spool member on which seat belt webbing is wound. The spool member is supported for rotation in a belt retraction direction and an opposite belt withdrawal direction. The retractor includes a plastically deformable torsion bar member having a first portion and a second portion. The second portion of the torsion bar member is rotatable relative to the first portion. The torsion bar member twists upon rotation of the second portion relative to the first portion.
The retractor includes an actuatable spool locking mechanism for, when actuated, blocking rotation of the spool member in the belt withdrawal direction. The spool locking mechanism includes a ratchet member and a pawl movable into locking engagement with the ratchet member to block rotation of the ratchet member. One of the spool member and the torsion bar member and the ratchet member has a spool cutter portion. The spool member is fixed for rotation with the first portion of the torsion bar member and the ratchet member is fixed for rotation with the second portion of the torsion bar member. The torsion bar member thereby resists rotation of the spool member relative to the ratchet member. The torsion bar member twists when the spool locking mechanism is actuated and tensile force from the seat belt webbing is applied to the spool member in an amount exceeding a predetermined amount. As the torsion bar member twists, the spool member rotates in the belt withdrawal direction relative to the ratchet member, and the cutter portion of the one member cuts into another one of the members to increase the resistance to rotation of the spool member relative to the ratchet member.